1. Field of the Invention
The present invention relates to a high definition television monitor for displaying video images reproduced from normal standard video signals such as NTSC standard video signals on a CRT display or a projection television display.
2. Description of the Related Art
For a so-called Hi-vision television, which is a popular name of the high definition television, a standard different from that of the NTSC standard, so far applied to normal televisions, has been defined. For example, in the NTSC standard, the number of scanning line is 525; the horizontal synchronizing frequency is 15.75 KHz; and the aspect ratio (the ratio of the height to the width of the screen) is 3:4, while for the high definition television, the number of scanning line is 1,125; the horizontal synchronizing frequency is 33.75 KHz, and the aspect ratio is 9:16. Therefore, for receiving television broadcasting images of the NTSC standard, the Hi-vision television receivers are generally constructed to perform the horizontal scanning not only at 33.75 KHz but also at 15.75 KHz or to perform the horizontal scanning at a frequency of about 33 KHz, where the NTSC standard video signal is converted to a signal at 31.5 KHz by signal processing such as interpolation, twice writing or the like.
However, in the former case, for performing the horizontal scanning additionally at 15.75 KHz, a horizontal deflection circuit must be provided for each frequency, and a switching circuit for high voltages is also necessary, thereby incurring a problem of a raised cost. In addition, in the latter case, a video image represented by one of two consecutive lines in the screen is the same as that of the previous line. Namely, the video image by one line widens to two lines on the screen for every field, causing the degradation of the image quality particularly with respect to the vertical resolution.